Cameron tells National Geographic News that his specially designed submarine called Deepsea Challenger completed the nearly 7-mile test dive Wednesday. The team returned to calmer waters and was headed back to the site Saturday.

Swiss engineer Jacques Piccard and U.S. Navy Capt. Don Walsh are the only other men to reach the spot. They spent about 20 minutes there during their 1960 dive but couldn't see much after their sub kicked up sand from the sea floor.